JP2007172967A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve safety of a battery at high temperatures by using an insulating board maintaining its shape even at abnormally high temperatures. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes a group of electrode consisting of a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode; a nonaqueous electrolyte; an insulating board arranged at the top and bottom of the group of electrodes; and a battery case having a bottom and an opening at the top for housing the group of the electrodes, the nonaqueous electrolyte and the insulating board, wherein the insulating board is formed of a bridged resin, and the bridging degree of the bridged resin is not less than 25%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte secondary battery, and more particularly, to a nonaqueous electrolyte secondary battery excellent in insulation between an electrode and a battery case or an external connection terminal. The nonaqueous electrolyte secondary battery of the present invention includes an inexpensive insulating plate that is excellent in shape maintainability even when the battery is abnormal.

  The performance of recent portable electronic devices such as mobile phones and portable information terminals greatly depends on the performance of the rechargeable secondary battery as well as the mounted semiconductor elements and electronic circuits. A secondary battery mounted on a portable electronic device is desired to be lighter and more compact at the same time as capacity is increased. As a secondary battery that meets these demands, a nickel-metal hydride storage battery having an energy density approximately twice that of a nickel cadmium storage battery has been developed. In addition, non-aqueous electrolyte secondary batteries that exceed the energy density of nickel metal hydride storage batteries, such as lithium ion batteries, have also been developed. These are properly used according to the application of the equipment used.

  In recent years, there has been an increasing demand for heat resistance and stability of nonaqueous electrolyte secondary batteries. The nonaqueous electrolyte secondary battery has an electrode group in which a positive electrode and a negative electrode are stacked via a separator, or a positive electrode and a negative electrode are wound in a spiral shape via a separator. The electrode group is housed in a cylindrical, rectangular, or flat battery case together with the nonaqueous electrolyte. In general, insulating plates are disposed above and below the electrode group in order to insulate the electrode group from the battery case or the external connection terminal.

  Since the insulating plate is accommodated in the battery, it is required to have excellent electrolyte resistance, hardness and strength in addition to the insulating property. Further, it is desirable that the insulating plate does not melt or flow even at an abnormally high temperature and maintains a function of preventing a short circuit between the electrode and the battery case or the external connection terminal.

Conventionally, the following has been proposed as a material for battery internal parts.
Patent Document 1 proposes to use polyethylene, polypropylene, ethylene polypropylene elastomer, styrene elastomer, olefin elastomer, ethylene propylene rubber, butyl rubber, styrene butadiene rubber and fluororubber having a specified surface hardness. Patent Document 2 proposes to use a network-like polyolefin resin having improved heat resistance by crosslinking between chain polymers with active silane groups. Patent Document 3 proposes to use a low-hardness rubber which is crosslinked with a peroxide and has a hardness of 50 or less. Patent Document 4 proposes to use a copolymer of propylene and ethylene having a prescribed bending elastic modulus. Patent Document 5 proposes to use an elastomer having a rebound elastic modulus. Patent Document 6 proposes to use polyimide, polyamide, fluororesin, silicone rubber, or a mixture thereof excellent in heat resistance for the sealing plate and the gasket. Patent Document 7 proposes to use a mixed material of an olefin resin that defines compression set and an olefin rubber or fluororubber. Patent Document 8 proposes to use a radiation cross-linked resin.

  By the way, a conventional insulating plate performs a predetermined function in a normal battery usage environment, but may not be able to maintain its shape at an abnormally high temperature. For example, when a battery is used in an abnormally high temperature environment due to user error, the battery may generate heat and the battery temperature may increase. In such a case, there is a possibility that the insulating plate melts and flows before the safety mechanism is activated, and a short circuit occurs between the electrode and the battery case or the external connection terminal.

Patent Document 9 proposes to use a composite of phenol resin and glass having excellent heat resistance. However, such a composite is hard and brittle. Therefore, in the battery assembling process, there is a disadvantage that crushed powder is generated by rubbing parts and the production yield is lowered.
JP 2000-149886 A Japanese Patent Laid-Open No. 61-051752 JP 2002-371161 A JP-A-7-130341 JP-A-7-288116 JP 2000-138041 A JP 2001-126684 A JP 2002-289158 A JP-A-8-64199

  An object of the present invention is to increase the stability of a battery at a high temperature by using an insulating plate that can maintain its shape even at an abnormally high temperature.

  The present invention relates to an electrode group comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, an insulating plate disposed above and below the electrode group, and an electrode group, a non-aqueous electrolyte, and an insulating plate. The present invention relates to a non-aqueous electrolyte secondary battery that includes a battery case with a bottom having an open top, and an insulating plate made of a crosslinked resin, and the degree of crosslinking of the crosslinked resin is 25% or more.

  Examples of the resin to be crosslinked include at least one selected from the group consisting of polyolefin resin, polyolefin elastomer, polyester resin, polyester elastomer, polyphenylene sulfide resin, polyarylate resin, polyamide resin, polyamide elastomer, fluororesin, and fluorinated elastomer. Can be used.

  According to the present invention, even at an abnormally high temperature, the possibility of an internal short circuit due to melting or flow of the insulating plate is reduced. Therefore, the safety when the nonaqueous electrolyte secondary battery is overcharged or used in an abnormal environment is improved.

The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrode group composed of a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, insulating plates disposed above and below the electrode group, and an electrode group. A bottomed battery case having an open top for housing the nonaqueous electrolyte and the insulating plate is provided.
However, the insulating plate is made of a crosslinked resin, and the crosslinking degree of the crosslinked resin is 25% or more.

  By setting the degree of cross-linking of the cross-linked resin to 25% or more, it is possible to maintain the shape of the insulating plate even at an abnormally high temperature. Therefore, an internal short circuit caused by melting or flow of the insulating plate is suppressed, and the safety of the nonaqueous electrolyte secondary battery is improved.

  The crosslinked resin does not need to be in a completely crosslinked state (a state where the degree of crosslinking is 100%). The crosslinked resin may be a composite of a crosslinked part and a non-crosslinked part. The degree of cross-linking is the weight ratio of the cross-linked portion to the total weight of the cross-linked resin (total of the cross-linked portion and the non-cross-linked portion). Therefore, the degree of crosslinking can be determined by the following method.

First, the weight W ₀ of the crosslinked resin sample is measured. This sample is immersed in a solvent under the condition that the non-crosslinked portion is completely dissolved. At this time, the non-crosslinked portion is completely dissolved in the solvent, and the crosslinked portion is not dissolved in the solvent but becomes a gel. When the resulting gel is separated, washed and dried, only the cross-linked part is obtained. Here, the weight W _d of the crosslinked portion is measured. The degree of cross-linking D is the formula (1):
D (%) = (W _d / W ₀ ) × 100
More demanded.

  The method for crosslinking the resin is not particularly limited. For example, the resin can be crosslinked by a method such as radiation crosslinking, silane crosslinking, or chemical crosslinking with a crosslinking agent. For example, various peroxides can be used as the crosslinking agent. Among these, radiation cross-linking is particularly preferable in terms of easy control of the degree of cross-linking and high productivity. Further, the radiation-crosslinked resin has a stable fluidity when being molded. Therefore, molding defects such as gelation and solidification due to a thermal crosslinking reaction are unlikely to occur during extrusion.

  The type of radiation used for radiation crosslinking is not particularly limited. For example, the resin can be crosslinked by irradiating the resin with β rays, γ rays, electron beams or X rays. Of these, electron beam irradiation is particularly preferred because of its relatively low cost and high output.

  Although the conditions for radiation crosslinking are not particularly limited, the radiation acceleration voltage is preferably in the range of 20 to 20000 keV, particularly preferably in the range of 100 to 12000 keV. The absorbed dose is preferably in the range of 2 to 2000 kGy, particularly preferably in the range of 10 to 700 kGy. When the acceleration voltage and absorbed dose of radiation are less than the lower limit of the above range, the effect of radiation crosslinking is reduced. Therefore, when the battery is abnormal, the insulating plate may not be able to maintain a sufficient shape. On the other hand, when the acceleration voltage and absorbed dose of radiation exceed the upper limit of the above range, the effect of radiation crosslinking may be excessive. Therefore, the elasticity of the crosslinked resin is lowered, and the impact strength (impact resistance) may be lowered. In addition, since a crosslinking characteristic is dependent on the kind of resin, it is desirable to optimize absorbed dose within the said range.

  For example, a crosslinked resin can be obtained by irradiating an inexpensive one-dimensional resin melted by heating with radiation. By irradiation with radiation, at least a part of the one-dimensional resin is cross-linked to change into a three-dimensional structure. As a result, the shape maintaining temperature of the insulating plate is improved.

  The shape maintenance temperature is a temperature at which the real part of the complex elastic modulus is less than the fourth power of 10 in the dynamic viscoelasticity measurement (TMA) of the crosslinked resin. When the atmospheric temperature exceeds the shape maintenance temperature, the insulating plate cannot maintain the shape. The shape maintenance temperature increases as the degree of crosslinking increases. However, if the degree of cross-linking becomes too high, the elasticity of the insulating plate is lowered and the impact strength is lowered. If the impact strength is reduced, the insulating plate may be crushed during the transfer of the insulating plate or during the battery assembly process, resulting in a defective process of the battery. Therefore, when setting the degree of crosslinking high, it is necessary to consider the balance with elasticity.

  When the degree of crosslinking is less than 25%, the shape maintaining temperature of the insulating plate is not sufficiently high. Thus, for example, at an ambient temperature of 250 ° C., the complex elastic modulus of the insulating plate may be less than 10 4, the insulating plate may melt, and an internal short circuit may occur. From the viewpoint of balancing the shape maintenance temperature and the elasticity, the degree of crosslinking is preferably 95% or less. A particularly preferred range for the degree of crosslinking is from 50% to 90%. Also, the shape maintaining temperature of the insulating plate should be higher than the melting temperature of the separator from the viewpoint of preventing a short circuit between the electrode group and the inner bottom surface of the battery case or the electrode group and the bottom surface of the sealing plate when the separator is melted. Is desirable. In addition, assuming that the battery is used in an abnormally high temperature environment due to the user's negligence, the shape maintaining temperature of the insulating plate is more preferably 250 ° C. or higher.

  When the degree of crosslinking is 25% or more, the shape maintaining temperature of the insulating plate measured by TMA is higher than the decomposition start temperature of the insulating plate measured by a thermogravimetric measuring device (TG). That is, the insulating plate proceeds with decomposition without undergoing a substantial fluid state even at a temperature at which thermal decomposition proceeds. For this reason, even if a battery becomes high temperature at the time of abnormality, an insulating plate does not melt. As a result, an internal short circuit due to melting of the insulating plate is suppressed.

  Examples of cross-linking resins include polyethylene resins, polypropylene resins, polyolefin resins such as cyclic polyolefin, polyester resins such as polyolefin elastomers and polyethylene terephthalate resins, polyester elastomers, polyphenylene sulfide resins, polyarylate resins, polyamide resins, polyamide elastomers, fluorine At least one selected from the group consisting of a resin and a fluorinated elastomer can be used. These resin may be used individually by 1 type, and may be used in combination of 2 or more type. For example, a polymer alloy or polymer blend in which two or more kinds of resins are combined may be used. Further, the resin may be used after being modified. For example, it is conceivable to substitute a functional group of the main chain or introduce an epoxy group or an acid anhydride. Among these resins, polyolefin resin is particularly preferable. The weight average molecular weight of the polyolefin resin before crosslinking is preferably, for example, 100,000 to 1,000,000.

The crosslinking of the resin is desirably performed after the resin is molded into a predetermined shape.
The resin may be used with a filler added as necessary. The filler is not particularly limited, and for example, glass fiber, talc, silica, potassium titanate and the like can be used.

FIG. 1 is a vertical cross-sectional view of an example of a nonaqueous electrolyte secondary battery including insulating plates disposed above and below an electrode group.
This battery has an electrode group in which a positive electrode 1 and a negative electrode 3 are wound in a spiral shape with a separator 5 interposed therebetween. The electrode group is accommodated in a bottomed battery case 8 having an open top. Insulating plates 6 and 7 are disposed above and below the electrode group. The electrode group is insulated by insulating plates 6 and 7 from a battery case 8 that also serves as a sealing plate having a positive electrode terminal and a negative electrode terminal.
An annular groove 9 is formed below the opening end of the battery case 8. A sealing plate is placed on the support portion bulged inward by the formation of the annular groove 9. An insulating gasket 11 is disposed on the peripheral edge of the sealing plate, and the opening end of the battery case 8 is caulked to the gasket 11.

  The sealing plate includes a plate 10 located at the lower part and a cap 15 located at the upper part of the plate 10. The plate 10 and the cap 15 are in a conductive state. The positive electrode lead 2 led out from the positive electrode 1 is welded to the plate 10. Therefore, the cap 15 is electrically connected to the positive electrode and functions as a positive electrode terminal (one of the external connection terminals). The negative electrode lead 4 led out from the negative electrode 3 is welded to the inner bottom surface of the battery case 8. Therefore, the battery case 8 becomes a negative electrode terminal (the other of the external connection terminals).

  The sealing plate is provided with a safety mechanism. The safety mechanism includes an upper valve body 12 and a lower valve body 13 disposed between the plate 10 and the cap 15. The upper valve body 12 and the lower valve body 13 are connected by a welding point 14 at the center. In the upper valve body 12 and the lower valve body 13, an easily destructible portion 12 a and an easily destructible portion 13 a are formed around the welding point 14, respectively. When the battery internal pressure rises abnormally, the easily breakable portion 13a is first broken. When the battery internal pressure further rises, the easily breakable portion 12a of the upper valve body 12 is broken, and the gas is discharged from the discharge hole 16 of the cap 15 to the outside. A PTC element 17 is disposed between the cap 15 and the upper valve body 12 in order to enhance safety.

In addition, the structure of the nonaqueous electrolyte secondary battery of this invention is not limited to the structure shown in FIG.
The positive electrode has, for example, a positive electrode current collector and a positive electrode active material layer carried thereon. For the positive electrode current collector, for example, a foil made of aluminum or aluminum alloy is used. The foil may be in a lathed or etched state. The thickness of the positive electrode current collector is generally 10 μm to 60 μm. The positive electrode active material layer is formed by applying a positive electrode mixture paste on one side or both sides of a positive electrode current collector, drying, and rolling. The positive electrode mixture paste is obtained by dispersing the positive electrode mixture in a liquid component. The positive electrode mixture includes a positive electrode active material as an essential component, and optionally includes a binder, a conductive agent, a thickener, and the like. Various dispersants, surfactants, stabilizers and the like may be added to the positive electrode mixture paste as necessary. The positive electrode current collector is provided with a plain portion that does not carry the positive electrode mixture, and the positive electrode lead is welded to the plain portion.

The positive electrode active material is not particularly limited. For example, a lithium-containing transition metal compound that can accept lithium ions as a guest is used. For example, a composite metal oxide of at least one transition metal selected from the group consisting of cobalt, manganese, nickel, chromium, iron, and vanadium and lithium is used. Among these, Li _x CoO ₂ , Li _x MnO ₂ , Li _x NiO ₂ , Li _x CrO ₂ , αLi _x FeO ₂ , Li _x VO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _{1- y O z, Li x Ni 1} -y M y O z, Li x Mn 2 O 4, and _{Li x Mn 2-y M y} O 4 ( where, M = Na, Mg, Sc , Y, Mn, Fe , Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B, at least one selected from the group consisting of x = 0 to 1.2, y = 0 to 0.9, z = 2 to 2. 3, x value is increased or decreased by charging and discharging). Transition metal chalcogenides, lithiated vanadium oxides and lithiated niobium oxides are also preferably used. These may be used alone or in combination of two or more. The average particle diameter of the positive electrode active material is preferably 1 μm to 30 μm.

  The negative electrode has, for example, a negative electrode current collector and a negative electrode active material layer carried thereon. For the negative electrode current collector, for example, a copper foil or a copper alloy foil is used. The foil may be in a lathed or etched state. The thickness of the negative electrode current collector is generally 10 μm to 50 μm. The negative electrode active material layer is formed by applying a negative electrode mixture paste on one side or both sides of a negative electrode current collector, drying, and rolling. The negative electrode mixture paste is obtained by dispersing the negative electrode mixture in a liquid component. The negative electrode mixture includes a negative electrode active material as an essential component, and optionally includes a binder, a conductive agent, a thickener, and the like. You may add various dispersing agents, surfactant, a stabilizer, etc. to a negative mix paste as needed. The negative electrode current collector is provided with a plain portion that does not carry the negative electrode mixture, and the negative electrode lead is welded to the plain portion.

  The negative electrode active material is not particularly limited, but it is preferable to use a carbon material that can release and occlude lithium ions during charging and discharging. For example, a fired body of an organic polymer compound (phenol resin, polyacrylonitrile, cellulose, etc.), a fired body of coke or pitch, artificial graphite, natural graphite, pitch-based carbon fiber, and PAN (polyacrylonitrile) -based carbon fiber are preferable. Although the shape of a carbon material is not specifically limited, A fibrous, spherical, scale-like, and massive thing can be used.

The binder, conductive agent, and thickener used for the positive electrode mixture and the negative electrode mixture can be the same as the conventional ones.
The binder is not particularly limited, but a binder that dissolves or disperses in the liquid component of the paste is used. For example, a fluororesin, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (SBR), acrylic polymer, and vinyl polymer can be used. These may be used alone or in combination of two or more. Among the fluororesins, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, and polytetrafluoroethylene are preferable. These fluororesins can be used as a dispersion (dispersion).

  As the conductive agent, for example, acetylene black, graphite and carbon fiber can be used. These may be used alone or in combination of two or more.

  As the thickener, ethylene-vinyl alcohol copolymer, carboxymethyl cellulose and methyl cellulose can be used. These may be used alone or in combination of two or more.

  Examples of the liquid component serving as a dispersion medium include water or warm water, N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethyl sulfoxide, hexamethylsulfuramide, tetramethylurea, acetone, Methyl ethyl ketone and cyclohexanone can be used. These may be used alone or in combination of two or more.

  The method for preparing the paste by dispersing the positive electrode mixture or the negative electrode mixture in the liquid component is not particularly limited, and for example, it can be prepared using a planetary mixer, a homomixer, a pin mixer, a kneader, and a homogenizer.

  The paste can be easily applied to the current collector using, for example, a slit die coater, reverse roll coater, lip coater, blade coater, knife coater, gravure coater or dip coater. The paste applied to the current collector is preferably naturally dried. However, from the viewpoint of productivity, it is preferable to dry at a temperature of 70 ° C. to 200 ° C. for 10 minutes to 5 hours.

  The positive electrode mixture or the negative electrode mixture supported on the current collector is rolled using, for example, a roll press. At this time, the thickness of the positive electrode or the negative electrode is adjusted to a predetermined thickness of 130 μm to 200 μm, for example. Rolling is preferably carried out a plurality of times at a linear pressure of 1000 to 2000 kg / cm, preferably by changing the linear pressure.

  A microporous film having a thickness of 15 to 30 μm is suitable for the separator. The microporous film may be a multilayer film composed of a plurality of layers. The material of the microporous film is not particularly limited, but for example, polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, poly Ether (polyethylene oxide or polypropylene oxide), cellulose (carboxymethyl cellulose or hydroxypropyl cellulose), poly (meth) acrylic acid, or poly (meth) acrylic acid ester can be used. These may be used alone or in combination of two or more. Of these, polyethylene, polypropylene, and polyvinylidene fluoride are preferable.

  Although the material of a battery case is not specifically limited, For example, copper, nickel, stainless steel, nickel plating steel etc. can be used. A battery case having a predetermined shape can be manufactured by drawing or DI processing on these materials. In order to enhance the corrosion resistance of the case, the processed battery case may be plated. In addition, by using a battery case made of aluminum or an aluminum alloy, a square nonaqueous electrolyte secondary battery having a light weight and a high energy density can be easily manufactured.

The nonaqueous electrolyte includes a nonaqueous solvent and a solute dissolved therein. The concentration of the solute contained in the nonaqueous electrolyte is preferably 0.5 to 1.5M.
The non-aqueous solvent preferably contains a cyclic carbonate and a chain carbonate as main components. The cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). The chain carbonate is preferably at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

As the solute, it is preferable to use a lithium salt having an anion having a strong electron-withdrawing property. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiC (SO ₂ CF ₃ ) ₃ are preferable. These may be used individually by 1 type and may be used in combination of 2 or more type.

  The material of the sealing plate and the gasket is not particularly limited, and the same materials as those in the past can be used. However, a material having resistance to a non-aqueous electrolyte and heat resistance is preferable. For example, it is preferable to use aluminum or an aluminum alloy for the plate 10 of FIG. A thin aluminum foil is suitable for the upper valve body 12 and the lower valve body 13.

  Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples. However, the following examples do not limit the present invention.

Example 1
(I) and LiCoO ₂ is produced positive electrode active material of the positive electrode, and carbon black as a conductive agent, and polytetrafluoroethylene (PTFE) as a binder, the weight ratio of 100: 3: mixed with 10, an appropriate amount A positive electrode mixture paste was prepared by kneading together with water. PTFE was used in an aqueous dispersion state. The positive electrode mixture paste was applied to both surfaces of a current collector made of an aluminum foil having a thickness of 15 μm by a doctor blade method and dried. The total thickness of the positive electrode mixture and the current collector after drying was about 220 μm. This was rolled to form a positive electrode active material layer, and a positive electrode plate having a thickness of 160 μm was obtained. A positive electrode having a predetermined size was cut out from the positive electrode plate, and an aluminum positive electrode lead was welded to a predetermined plain portion.

(Ii) Production of negative electrode Graphite, which is a negative electrode active material, and styrene butadiene rubber (SBR), which is a binder, are mixed at a weight ratio of 100: 5 and kneaded together with an appropriate amount of water to form a negative electrode mixture paste. Was prepared. The negative electrode mixture paste was applied to both surfaces of a current collector made of a copper foil having a thickness of 12 μm by a doctor blade method and dried. The total thickness of the negative electrode mixture and the current collector after drying was about 230 μm. This was rolled to form a negative electrode active material layer, and a negative electrode plate having a thickness of 170 μm was obtained. A negative electrode having a predetermined size was cut out from the negative electrode plate, and a nickel negative electrode lead was welded to a predetermined plain portion.

(Iii) Production of Insulating Plate A polyethylene having a weight average molecular weight of 300,000 was formed into a disk shape to produce a pair of insulating plate precursors. Thereafter, the precursor of the insulating plate was irradiated with an electron beam to obtain a pair of insulating plates.
The weight (W ₀ ) of the obtained insulating plate was measured. Then, the insulating plate was immersed in 120 degreeC hot xylene for 24 hours, and the non-bridge | crosslinking part contained in an insulating plate was eluted in hot xylene. Thereafter, the remaining gel-like crosslinked portion was washed and dried, and the weight (W _d ) was measured. Then, the calculated degree of crosslinking _{D = (W d / W 0} ) × 100, was D = 95%.

(Iv) Battery assembly A sealed battery similar to that shown in FIG. 1 was assembled in the following manner.
The positive electrode and the negative electrode were spirally wound through a separator made of a polyethylene microporous film having a thickness of 25 μm to constitute an electrode group. The above-mentioned insulating plates were arranged above and below the electrode group, respectively, and housed in a bottomed battery case having an open top. Thereafter, the inner bottom portion of the battery case and the negative electrode lead were connected via a lower insulating plate. Next, an annular groove was formed below the opening end of the battery case, and a sealing plate with a gasket around it was placed on the support that bulged inward. The positive electrode lead was welded to a plate located under the sealing plate. The sealing plate has a structure similar to that shown in FIG. After pouring a predetermined amount of nonaqueous electrolyte into the battery case, the open end of the battery case was caulked to the gasket. The compression ratio of the gasket was 30%. Thus, a cylindrical nonaqueous electrolyte secondary battery having a diameter of 18.0 mm and a total height of 65.0 mm and a battery capacity of 2000 mAh was completed.

The nonaqueous electrolyte is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a molar ratio of 1: 3, and lithium hexafluorophosphate (LiPF ₆ ) as a solute at a concentration of 1 mol / L. What was melt | dissolved in was used.

Example 2
In the production of the insulating plate, a sealed battery was produced in the same manner as in Example 1 except that the electron beam irradiation conditions were changed and the degree of crosslinking of the insulating plate was 78%.

Example 3
In the production of the insulating plate, a sealed battery was produced in the same manner as in Example 1 except that the electron beam irradiation conditions were changed and the degree of crosslinking of the insulating plate was 52%.

Example 4
In the production of the insulating plate, a sealed battery was produced in the same manner as in Example 1 except that the electron beam irradiation conditions were changed and the degree of crosslinking of the insulating plate was 25%.

Example 5
In the production of the insulating plate, instead of polyethylene, Terralink N6N01A (cross-linked nylon 6 / mineral reinforced) manufactured by Sumitomo Electric Industries, Ltd. was used, and the degree of cross-linking of the insulating plate was set to 70%. Similarly, a sealed battery was produced.

<< Comparative Example 1 >>
In the production of the insulating plate, a sealed battery was produced in the same manner as in Example 1 except that the electron beam irradiation conditions were changed and the degree of crosslinking of the insulating plate was 20%.

<< Comparative Example 2 >>
In the production of the insulating plate, a sealed battery was produced in the same manner as in Example 1 except that polypropylene was used instead of polyethylene and the polypropylene was not subjected to radiation crosslinking (that is, the degree of crosslinking was 0%).

[Evaluation]
The batteries of each Example and each Comparative Example were subjected to predetermined activation and preliminary charge / discharge.
Thereafter, each battery was subjected to constant current charging at an environmental temperature of 20 ° C. under conditions of a maximum current of 1000 mA and a charge end voltage of 4.2 V, and then constant voltage charge was performed to a stop current of 100 mA.
For each example and each comparative example, 20 fully charged batteries were prepared. These batteries were introduced into a thermostatic chamber set at a temperature of 150 ° C., and the number n of batteries in which abnormal heat generation due to an internal short circuit occurred during one hour was examined. The results are shown in Table 1.
Thereafter, the temperature of the thermostatic bath was changed to 170 ° C. and 250 ° C., and the same evaluation as described above was performed. The results are shown in Table 1.

  As shown in Table 1, the batteries of Examples 1 to 5 using an insulating plate having a degree of crosslinking of 25% or more did not generate any abnormal heat even at an abnormally high temperature of 250 ° C. When the battery after evaluation was disassembled and the state of the insulating plate was confirmed, the insulating plates of the batteries of Examples 1 to 5 maintained their shapes. On the other hand, it was found that the insulating plates of the batteries of Comparative Examples 1 and 2 were melted and the shape was not maintained. It is thought that this caused an internal short circuit of the battery and abnormal heat generation.

Example 6
In the production of the insulating plate, instead of polyethylene, Terralink OEN05A (crosslinked polyolefin elastomer / non-reinforced) manufactured by Sumitomo Electric Industries, Ltd., which is a polyolefin elastomer, was used, except that the degree of crosslinking of the insulating plate was 70%. A sealed battery was produced in the same manner as in Example 1.

Example 7
In the production of the insulating plate, instead of polyethylene, using Teralink BTN01A (cross-linked PBT (polybutylene terephthalate) / glass reinforced) manufactured by Sumitomo Electric Industries, Ltd., which is a polyester resin, the cross-linking degree of the insulating plate is set to 60%. A sealed battery was produced in the same manner as in Example 1 except that.

Example 8
In the production of the insulating plate, instead of polyethylene, using Terralink EEN05A (crosslinked polyester elastomer / non-reinforced) manufactured by Sumitomo Electric Industries, which is a polyester elastomer, the degree of crosslinking of the insulating plate is 65%, A sealed battery was produced in the same manner as in Example 1.

Example 9
In the production of the insulation board, instead of polyethylene, we used Terralink AEN05A (crosslinked nylon / non-reinforced) manufactured by Sumitomo Electric Industries, Ltd., which is a polyamide elastomer, except that the degree of crosslinking of the insulation board was 70%. A sealed battery was produced in the same manner as in Example 1.

Example 10
In the production of the insulating plate, instead of polyethylene, teralink VFF01A (crosslinked PVDF (polyvinylidene fluoride) / non-reinforced) manufactured by Sumitomo Electric Industries, Ltd., which is a fluororesin, is used, and the degree of crosslinking of the insulating plate is 65%. A sealed battery was produced in the same manner as in Example 1 except that.

Example 11
In the production of the insulating plate, instead of polyethylene, except for using terrain FEF05A (cross-linked PVDF / non-reinforced) manufactured by Sumitomo Electric Industries, which is a fluorinated elastomer, the degree of cross-linking of the insulating plate is 60%, A sealed battery was produced in the same manner as in Example 1.

  The batteries of each example were evaluated in the same manner as described above. The results are shown in Table 2.

  As shown in Table 2, the batteries of Examples 6 to 11 using an insulating plate having a degree of crosslinking of 25% or more did not generate any abnormal heat even at an abnormally high temperature of 250 ° C. When the battery after evaluation was disassembled and the state of the insulating plate was confirmed, the insulating plates of the batteries of Examples 6 to 11 maintained their shapes.

  The present invention is suitable for application to, for example, a non-aqueous electrolyte secondary battery that requires high safety even at abnormally high temperatures. The present invention can be applied to various non-aqueous electrolyte secondary batteries. For example, non-aqueous electrolyte secondary batteries serving as driving power sources for consumer electronic devices, portable information terminals, portable electronic devices, portable devices, cordless devices, and the like. Applicable to batteries. The present invention is also applicable to a power source for a small household electric power storage device, a motorcycle, an electric vehicle, a hybrid electric vehicle, and the like. The shape of the battery is not particularly limited. For example, the present invention can be used for any shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a flat shape, and a square shape. The form of the electrode plate group is not limited, and the present invention can be applied to any form such as a wound type and a laminated type. The size of the battery is not limited, and the present invention can be used for any size such as small, medium, and large.

It is a longitudinal cross-sectional view of an example of the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode lead 3 Negative electrode 4 Negative electrode lead 5 Separator 6, 7 Insulation board 8 Battery case 9 Annular groove 10 Plate 11 Insulation gasket 12 Upper valve body 12a, 13a Easily breakable part 13 Lower valve body 14 Welding point 15 Cap 16 Discharge hole 17 PTC element

Claims (2)

An electrode group comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;
Non-aqueous electrolyte,
Insulating plates disposed above and below the electrode group, and a bottomed battery case having an open upper portion for accommodating the electrode group, the nonaqueous electrolyte and the insulating plate,
The insulating plate is made of a crosslinked resin,
A non-aqueous electrolyte secondary battery in which the degree of cross-linking of the cross-linked resin is 25% or more. The resin is composed of at least one selected from the group consisting of polyolefin resin, polyolefin elastomer, polyester resin, polyester elastomer, polyphenylene sulfide resin, polyarylate resin, polyamide resin, polyamide elastomer, fluororesin, and fluorinated elastomer. The nonaqueous electrolyte secondary battery according to 1.

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